Conventionally, flanged articles having a flange stretching out of its periphery are used in various industrial application fields. An example of the flanged articles is a center pillar reinforce of a car. This center pillar reinforce serves to protect the persons in the car on collision from a lateral side by reducing the collision force (impact force). For the reduction of the collision impact, the center pillar reinforce is sometimes partly quench-hardened, not entirely, for dispersing the collision impact.
The center pillar reinforces are produced by press-forming. Various techniques have been disclosed for the hardening of the worked parts like the press-formed articles (e.g., JP-A-54-78311, JP-A-4-72010, JP-A-6-330165, and JP-A-10-17933 (“JP-A” herein means Japanese Patent Application Laid-Open Publication)).
Of these Patent Application Laid-Open Publications, JP-A-54-78311 discloses a technique of irradiation of a working object with a laser beam to harden locally the irradiated portion. This technique is shown to be capable of hardening only a limited portion of the working object.
JP-A-4-72010 discloses a technique of irradiation of a press-formed product with high-density energy like a laser beam at the strength-requiring portion only to harden the irradiated portion. This technique is shown, like the above technique, to be capable of hardening only a limited portion of the working object.
JP-A-6-330165 discloses a technique of hardening a flat plate and press-molding this hardened plate. With this technique, the deformation caused by the hardening is corrected by press-forming.
JP-A-10-17933 discloses a technique of hardening to cause local change of the hardness in the press-formed product. This technique is shown to give mountain-shaped hardness distribution to improve impact energy absorbency.
Of the above four JP-A disclosures, the three except JP-A-330165 consider little the possible deformation caused after the quench-hardening. Therefore, these techniques can cause significant deformation of a press-formed product of a thin plate.
With the technique disclosed in JP-A-330165, the degree of bending of the plate is limited since the flat plate is press-formed after hardening.
On the other hand, a technique is disclosed (Materia Japan, Vol. 37, No. 6 (1998)) by which a flanged article like a center pillar reinforce is hardened with the flange forcibly deformed elastically by fixing (clamping) by a clamping device. By this technique, firstly the flanged article is hardened with the flange clamped. After the hardening, springback displacement of the unclamped article is recorded. The height of the support for the flanged article is adjusted to cause the same extent of displacement in the reverse direction to cause elastic deformation of the flange, and in this deformed state, hardening is conducted. After the hardening, the unclamped flanged article does not have deformation. Such a technique is described in the above report.
In the above technique of deforming the flange elastically, however, the flange is clamped at constant intervals. The flange may have less rigid portion depending on its shape, so that the flange can be broken at this less rigid portion. In particular, an article obtained by press-forming of a thin plate is liable to be broken.